[PSIG]

Looking for options to provide startup spark for engines without electric starters. Kick-start bikes, pull-start sleds, prop-start aircraft, etc, that do not have substantial rotation for sync in one cranking "stroke".

Perhaps an option to trigger spark from the cycle (cam) signal, when below cranking rpm threshold, regardless of the crank tooth count. The firing would be instant on chosen signal (trigger return), and would require the ability to place the cycle signal at startup timing location. It likely could only work with 1-tooth cycle signals, assuming more teeth would require more rotation than available.

In my head, this single cylinder firing would 'kick' a longer rotation in order to gain sync and continue run. If approaching compression could not be felt, an LED could be used to pre-position the crank before the kick or pull, in order to pass the cycle signal during the stroke.

If that makes sense, a version to fire on missing-tooth crank gap could also work for multi-cylinder waste-spark setups, with similar requirements. I am assuming an offset reference (e.g., -35° from CPS tooth edge) is of limited use, as we don't have the rotation in order to determine crank speed and angles, yet.

Thoughts or alternative ideas, anyone?

[jonbill]

Couldn't you use 'fix cranking timing with trigger' feature?

[jonbill]

I guess that needs sync before it'll work.

[jonbill]

How many cylinders do these engines typically have? 1 or 2?

[PSIG]

While it could have any cylinder count, I would expect 1 to 4 cylinders most commonly. Types that would have manual cranking, so no electric continuous cranking to find sync. Fix Cranking Timing to Trigger (trigger return) could be the basis, just on the cycle signal, TDC signal, or missing tooth perhaps.

[jonbill]

I was thinking that if you didn't necessarily have a cam signal, you could use the secondary to read 2 crank speed teeth 180 apart and fire all ign channels at once when either tooth is seen.
With low cylinder counts, I was thinking the timing on the "wrong" cylinders would be too far out to do any harm.

[PSIG]

Indeed, that could work well on 180° cranks and limited cylinders, to same effect as wasted-spark. Hmm. I imagine a truth-table in the Wiki would be necessary for clarity of useful combinations.

[LPG2CV]

Probably a simple enough thing to code, but you would also need to ensure fuel was available with low rpm. I believe fuel is cut <50 rpm

Edit

Though saying that. That is around one revolution per second, and you would hope to achieve that with a non electrical start.

[jonbill]

Problem is, you haven't got a measured rpm because you haven't got sync yet - so proper fueling won't happen. I think it would have to fire on fuel supplied by the priming pulse.

[PSIG]

Thanks for each response. Indeed, only priming would have occurred prior to spark firing, so the first firing would rely on existing fuel (if warm restart) plus priming (warm or cold start). It is not stated anywhere, but Speeduino effectively requires electric start currently, especially for low cylinder counts.

The goal IMO is to fire and accelerate the crank to gain sync for fuel and spark to continue the run. My current direction is to provide that first spark and resulting energy to jump towards the other requirements to run. That first-firing may be the golden egg that leads to everything following, e.g., older carb and points motorcycles where first firing carries it to the next.

To restate the obvious, this would be easy with direct-triggering of one tooth-per-cylinder, a distributor, or designating triggering teeth. However, in our quest for greater resolution, we lose some of those options using 12-1, 60-2, 36/1, etc. Looking for a scheme to allow triggered first or few sparks and simultaneous or quick sync for continued run, within a forest of desired higher tooth counts.

I am not leading a crusade, but offering to collect and display viable options here, as a menu for dev's to hopefully use in creating a simple and effective solution. More thoughts welcome!